1 For a Title this Psalm has, “Unto the end for the presses, on the fifth of the Sabbath, a Psalm to Asaph himself.” Into one title many mysteries are heaped together, still so that the lintel of the Psalm indicates the things within. As we have to speak of the presses, let no one expect that we shall speak of a vat, of a press, of olive baskets; because neither the Psalm has this, and therefore it indicates the greater mystery....
No such thing did ye hear in this when it was reading. Therefore take the presses for the mystery of the Church, which is now transacting. In the presses we observe three things, pressure, and of the pressure two things, one to be laid up, the other to be thrown away. There takes place then in the press a treading, a crushing, a weight: and with these the oil strains out secretly into the vat, the lees run openly down the streets.
Look intently on this great spectacle. For God ceases not to exhibit to us that which we may look upon with great joy, nor is the madness of the Circus to be compared with this spectacle. That belongs to the lees, this to the oil. When therefore ye hear the blasphemers babble impudently and say that distresses abound in Christian times; for you know that they love to say this: and it is an old proverb, yet one that began from Christian times, “God gives no rain; count it to the Christians!” Although it was those of old that said thus. But these now say also, “That God sends rain, count it to the Christians! God sends no rain; we sow not. God sends rain; we reap not!” And they wilfully make that an occasion of showing pride, which ought to make them more earnest in supplication, choosing rather to blaspheme than to pray.
When therefore they talk of such things, when they make such boasts, when they say these things, and say them in defiance, not with fear, but with loftiness, let them not disturb you. For suppose that pressures abound; be thou oil. Let the lees, black with the darkness of ignorance, be insolent; and let it, as though cast away in the streets, go gibing publicly: but do thou by yourself in your heart, where He who sees in secret will requite you, strain off into the vat....To name some one thing about which even they murmur who make them: How great plunderings, they say, are there in our times, how great distresses of the innocent, how great robberies of other men's goods! Thus indeed you take notice of the lees, that other men's goods are seized; to the oil you give no heed, that to the poor are given even men's own. The old time had no such plunderers of other men's goods: but the old time had no such givers of their own goods....
Source: The Enarrations, or Expositions, on the Psalms (New Advent)